Infectious Diseases Practice Questions

Q: Chandler's endemic index is used in the diagnosis or assessment of which condition?

Hookworm infestation. **Explanation:** **Chandler’s Index** is a specific epidemiological tool used to assess the **severity of Hookworm infestation** in a community. Unlike simple prevalence rates, this index measures the "worm burden" by calculating the **average number of eggs per gram (EPG) of stool** across a population sample. * **Why it is correct:** Hookworm pathogenicity is directly related to the number of worms present (intensity of infection) rather than just their presence. Chandler’s Index categorizes the public health significance: an index below 200-250 is considered low, while an index above 500 indicates a significant public health problem where clinical hookworm anemia is likely prevalent. **Analysis of Incorrect Options:** * **A. Dengue Hemorrhagic Fever:** Monitored using entomological indices like the House Index, Container Index, and Breteau Index (measuring *Aedes aegypti* density). * **B. Malaria:** Assessed using the Annual Parasite Incidence (API), Annual Blood Examination Rate (ABER), and Splenic Index. * **C. Cholera:** Monitored through surveillance of "Acute Diarrheal Diseases" and confirmed via stool culture (Gold Standard) or the presence of "Rice water stools." **High-Yield Clinical Pearls for NEET-PG:** * **Hookworm Species:** *Ancylostoma duodenale* (causes more blood loss, ~0.15ml/day) and *Necator americanus* (~0.03ml/day). * **Clinical Feature:** The hallmark is **Iron Deficiency Anemia** (Microcytic Hypochromic). * **Treatment of Choice:** Albendazole (400mg single dose). * **Public Health Strategy:** Periodic deworming (National Deworming Day) and improving sanitation to prevent skin penetration (Ground itch).

Q: Which type of mosquito is depicted?

Culex. ***Culex*** - Female **palpi are shorter** than the proboscis, as visible in the depicted mosquito. - Wings are **unspotted**, distinguishing it from Anopheles. - Lacks the **white/silver banding** on legs and abdomen characteristic of Aedes. - Wings show **uniform brown scales without the distinctive pale and dark scale patches** seen in Mansonoides, providing a positive visible feature distinguishing Culex from Mansonoides in the image. *Anopheles* - Female **palpi are equal in length** to the proboscis and wings often have **spotted patterns**. - Characteristic **45-degree resting posture** with head and proboscis angled downward. *Aedes* - Distinguished by **white/silver bands** on legs and abdomen, creating a striped appearance — absent in the depicted mosquito. - Has **short palpi** compared to proboscis length. *Mansonoides* - Less commonly encountered genus with **palpi shorter** than proboscis in females. - Lacks the characteristic **angled resting posture** and **wing spotting** of Anopheles. - Distinguished from Culex by **mottled wing scales** (alternating pale and dark patches on the wings) — absent in the depicted mosquito, which shows plain, uniformly scaled wings.

Q: Man is the dead-end host for which of the following infections?

Rabies, Tetanus. ### Explanation **1. Understanding the Concept: Dead-end Host** A **dead-end host** (or incidental host) is an organism from which an infectious agent cannot be transmitted to another susceptible host. This usually occurs because the pathogen does not reach a sufficient concentration in the blood (viremia/bacteremia) or tissues to be picked up by a vector or shed into the environment to continue its life cycle. **2. Why Option D is Correct** * **Rabies:** Humans are infected through the bite of a rabid animal (usually a dog). While the virus travels to the human brain, humans do not typically bite other humans or animals to transmit the virus further. Thus, the chain of transmission ends with the human. * **Tetanus:** *Clostridium tetani* spores enter the body through contaminated wounds. The bacteria produce toxins locally; however, tetanus is **not communicable** from person to person. The bacteria are not shed from the patient to infect others. **3. Why Other Options are Incorrect** * **Measles (Options A & B):** Humans are the **only reservoir** and the primary source of infection. It is highly contagious via respiratory droplets. Humans are definitely not dead-end hosts here. * **Yellow Fever (Options B & C):** In the **Urban Cycle**, humans serve as a reservoir where the *Aedes aegypti* mosquito picks up the virus from an infected person and transmits it to another. Therefore, humans are part of the active transmission cycle. **4. NEET-PG High-Yield Pearls** * **Other Dead-end Hosts:** Humans are also dead-end hosts for **Japanese Encephalitis (JE)**, **Hydatid Disease** (*Echinococcus granulosus*), and **Trichinellosis**. * **JE Exception:** In Japanese Encephalitis, the **pig** is the "amplifier host," and the **Ardeid bird** is the "natural reservoir," while the human is the dead-end host. * **Tetanus Key Fact:** It is the only infectious disease that is **non-communicable** but vaccine-preventable.

Q: What is the standard dose of purified protein derivative (PPD) for the Mantoux test?

5 TU. ### Explanation **Correct Option: A (5 TU)** The standard Mantoux test (Tuberculin Skin Test) utilizes **5 Tuberculin Units (TU)** of Purified Protein Derivative (PPD). In the standard procedure, 0.1 ml of PPD-S (Standard) or its equivalent (e.g., PPD RT23 with Tween 80) is injected **intradermally** on the volar aspect of the forearm using a tuberculin syringe. This dose is calibrated to provide high sensitivity and specificity for detecting *Mycobacterium tuberculosis* infection while minimizing non-specific cross-reactions. **Why Incorrect Options are Wrong:** * **B (10 TU):** While 10 TU was historically used in some regions or for specific research protocols, it is not the current global standard recommended by the WHO or the National Tuberculosis Elimination Program (NTEP). Using 10 TU increases the risk of false-positive results due to cross-reactivity with non-tuberculous mycobacteria (NTM). * **C & D (15 TU & 20 TU):** These doses are excessively high. They would lead to significant local tissue necrosis and severe inflammatory reactions, making the test results uninterpretable and clinically unsafe. **High-Yield Clinical Pearls for NEET-PG:** * **Reading the Test:** Results must be read **48 to 72 hours** after administration. * **Measurement:** Only the **induration** (palpable hardness) is measured transverse to the long axis of the arm, not the erythema (redness). * **Interpretation (NTEP India):** An induration of **≥10 mm** is generally considered positive. In HIV-positive individuals or severely malnourished children, **≥5 mm** is considered positive. * **False Negatives:** Can occur in miliary TB, malnutrition, sarcoidosis, and viral infections like Measles or HIV (Anergy). * **BCG Vaccine:** Prior BCG vaccination can cause a false positive, though the reaction usually wanes after several years.

Q: What is the true infectivity period of hepatitis A?

2-3 weeks before and 1 week after the onset of jaundice. **Explanation:** The infectivity of Hepatitis A Virus (HAV) is closely linked to the concentration of the virus excreted in the feces. The maximum viral shedding occurs during the late incubation period and the prodromal (pre-icteric) phase. **1. Why Option D is Correct:** According to standard epidemiological data (Park’s PSM), the period of maximum infectivity for Hepatitis A begins **2 to 3 weeks before** the onset of jaundice and continues for about **1 week after** the appearance of jaundice. By the time jaundice is clinically apparent, the viral titer in the stool begins to decline rapidly, and most patients are non-infectious by the end of the first week of the icteric phase. **2. Analysis of Incorrect Options:** * **Options A & C:** These suggest a 2-week post-jaundice infectivity period. While viral RNA can sometimes be detected longer, the "true infectivity" (the period where transmission is epidemiologically significant) typically ceases after 7 days of jaundice. * **Option B:** This underestimates the pre-icteric infectivity. The virus starts shedding significantly as early as 2-3 weeks before symptoms appear, making this the most dangerous period for community transmission. **3. High-Yield Clinical Pearls for NEET-PG:** * **Mode of Transmission:** Primarily feco-oral; common in areas with poor sanitation. * **Secondary Attack Rate (SAR):** High among household contacts (approx. 20%). * **Diagnosis:** IgM anti-HAV is the gold standard for acute infection. * **Vaccination:** Live attenuated (H2 strain) or Inactivated vaccines are available. * **Post-exposure Prophylaxis:** Best given within 2 weeks of exposure (Vaccine or Immunoglobulin). * **Key Fact:** Hepatitis A does **not** cause chronic infection or a carrier state.

Q: Which of the following is NOT a component of the SAFE strategy?

Screening. The **SAFE strategy** is a comprehensive public health approach recommended by the WHO for the global elimination of **Trachoma** (caused by *Chlamydia trachomatis*). ### Why "Screening" is the Correct Answer The letter **'S'** in the SAFE acronym stands for **Surgery**, not Screening. While screening is a general public health activity, it is not a formal component of this specific management protocol. The goal of the 'S' component is to provide surgical correction (typically Bilamellar Tarsal Rotation) for individuals suffering from **trachomatous trichiasis** to prevent corneal opacity and blindness. ### Explanation of Incorrect Options * **Antibiotics (A):** This refers to the mass distribution of antibiotics (specifically **Azithromycin** 20mg/kg single dose or Tetracycline 1% eye ointment) to the entire community to treat active infection and reduce the reservoir of *C. trachomatis*. * **Facial hygiene (F):** This focuses on encouraging children and adults to wash their faces regularly. Clean faces reduce the transmission of infected ocular and nasal secretions. * **Environmental modification (E):** This involves improving access to clean water, proper sanitation, and **fly control** (specifically *Musca sorbens*), as flies are the primary mechanical vectors for the disease. ### High-Yield Clinical Pearls for NEET-PG * **Target Goal:** The WHO aims for the Global Elimination of Trachoma by the year **2030**. * **Vector:** *Musca sorbens* (the eye-seeking fly) is the most common vector. * **Drug of Choice:** Oral Azithromycin (Single dose) is the preferred treatment in the SAFE strategy. * **Trachoma Grading:** Remember the **WHO FISTO classification** (Follicular, Intense, Scarring, Trichiasis, Opacity) for clinical staging.

Question 1

Which of the following statements about leprosy is false?

Accepted Answer

MDT is contraindicated during pregnancy.

Answer

It has been eliminated from India.

Answer

It can be transmitted through breast milk.

Answer

Lepromin test is not a diagnostic test.

Question 2

Chandler's endemic index is used in the diagnosis or assessment of which condition?

Accepted Answer

Hookworm infestation

Answer

Dengue hemorrhagic fever

Answer

Malaria

Answer

Cholera

Question 3

Which type of mosquito is depicted?

Accepted Answer

Culex

Answer

Aedes

Answer

Anopheles

Answer

Mansonoides

Question 4

What is the microfilaria endemicity index?

Accepted Answer

% of persons showing microfilaria in blood among diseased individuals

Answer

% of persons showing microfilaria in blood

Answer

Number of microfilaria in the blood

Answer

Average number of persons with positive slides

Question 5

Man is the dead-end host for which of the following infections?

Accepted Answer

Rabies, Tetanus

Answer

Tetanus, Measles

Answer

Measles, Yellow fever

Answer

Tetanus, Yellow fever

Question 6

Management of non-immunized diphtheria contacts includes all of the following except:

Accepted Answer

Prophylactic penicillin, daily throat examinations, and throat swab culture

Answer

Prophylactic penicillin and throat swab culture

Answer

Prophylactic penicillin and daily throat examinations

Answer

Single dose of toxoid and throat swab culture

Question 7

What is the standard dose of purified protein derivative (PPD) for the Mantoux test?

Accepted Answer

5 TU

Answer

10 TU

Answer

15 TU

Answer

20 TU

Question 8

An adult male patient presented with cough and fever for 3 months and intermittent haemoptysis. His sputum was positive for AFB. He had previously received 3 weeks of RHZE treatment from a nearby hospital before discontinuing it. How will you categorize and manage this patient?

Accepted Answer

Category I, treatment regimen (RHZ) for 3 months

Answer

Category III, treatment regimen (RHZ) for 3 months

Answer

Category II, treatment regimen (RHZ) for 3 months

Answer

Category II, treatment regimen (RHZ) for 3 months

Question 9

What is the true infectivity period of hepatitis A?

Accepted Answer

2-3 weeks before and 1 week after the onset of jaundice

Answer

1-2 weeks before and 2 weeks after the onset of jaundice

Answer

1-2 weeks before and 1 week after the onset of jaundice

Answer

2-3 weeks before and 2 weeks after the onset of jaundice

Question 10

Which of the following is NOT a component of the SAFE strategy?

Accepted Answer

Screening

Answer

Antibiotics

Answer

Facial hygiene

Answer

Environmental modification

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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